Tuberculosis control can be improved by targeting specific measures to specific populations. Chemoprophylaxis is the most efficient intervention for populations in which disease results from reactivated latent infection. Whereas case finding and treatment is more appropriate for those with considerable ongoing transmission. Currently, these measures are allocated based on the degree of, development of a country. Chemoprophylaxis used in developed countries and case finding in developing countries. In San Francisco we have integrated DNA fingerprinting techniques with conventional epidemiologic investigations to distinguish between reactivated and recently transmitted tuberculosis. In addition to targeting control strategies, this approach has yielded useful insights into the detailed epidemiology of tuberculosis transmission. We now propose to use this molecular approach to describe the epidemiology of transmitted and reactivated disease in the State of Chiapas, which has a tuberculosis rate that is almost three times greater than the Mexican national average. This approach should permit the precise targeting of these two basic control measures to specific subpopulations. In addition, detailed investigation of those patients who have been recently infected with tuberculosis will identify modifiable risk factors for tuberculosis transmission in tropical and developing regions of the world where tuberculosis is a major public health problem. Additionally, it is anticipated that this collaborative effort between basic scientists, clinicians, epidemiologists and public health officials from Chiapas, Mexico City, and the United States will result in the transfer of appropriate technologies to Mexico and strengthen tuberculosis control.